It is known that for communication between connected network devices, unicast messages (or point-to-point messages) or unicast communication can be used. Unicast messages allow to individually address a single device in the network by a sender. If the addressed device receives a message, it typically sends back to the sender an acknowledgement message (ACK). In case the acknowledgement is received, the sender knows that the sent message was well received. Also, a non-acknowledgement message (NACK) can be sent by the receiver, in case the message was not well-received, e.g. could not be decoded or was only partially received. In case of an non-acknowledgement message or in case the acknowledgement message is not received by the sender or is not received in a specified time period, the sender knows or expects that something went wrong and may re-send the message. This way of communication provides a highly reliable network communication as the procedure ensures that all messages or network (IP, internet protocol) packages are received by a receiver.
However, addressing a high number of devices using unicast messages by the sender leads to sending messages in a consecutive or sequential manner and hence, from the point in time the sender sends the message to a first addressed device, to the time the last addressed device receives the message a lot of time passes.
Therefore, for example, if the devices are lighting units such as luminaires, using unicast communication leads to latencies which means that not all building technology devices receive a message at the same time. If the building technology devices are, e.g., activated by the message sent from the sender, not all building technology devices are switched on simultaneously, or at the same time, but will, depending on the addressing scheme, may be activated randomly or in a sequence depending on their assigned addresses.
Sending messages to all or a group of building technology devices and waiting for individual acknowledgements suffers from two problems: Firstly the different end points receive the messages at different points in time and this affects synchronization of the building technology devices. Secondly the latency of message reception increases as the number of building technology devices addressed increases. This results in poor system performance.
Thus, a control of all or a group of building technology devices is needed such as point-to-multipoint communication of or a multipoint-to-multipoint communication. The message issuing building technology device can be a single sender, master, control unit, etc. Such communication is often achieved by either broadcasting messages to all devices connected to the sender by e.g. a single wired bus, or by flooding a wireless network. Examples of such techniques include DALI group communication, IPv6 multicast, IPv4 broadcast. Each building technology has an address which identifies the building technology device. An additional multicast or broadcast address can be defined to address a portion or all devices of a network (cf. common networking approaches using IPv4 and/or IPv6).
However, multicast, broadcast and unicast methods have limitations when applied to the problem of group communication in building technology systems. With multicast or broadcast methods, the initial message is sent from a building technology device issuing a message to multiple building technology devices at the same time, which are received by the destination devices at approximately the same time. Due to the nature of multicast or broadcast message sending, the do not acknowledge the receipt of the message by replying to the issuing building technology device.
If the message is sent via an unreliable communication medium such as an IPv6 over wireless network, it cannot be guaranteed that all destination devices receive the transmitted message. Therefore, multicast or broadcast messages only provide an unreliable means of communication. Even though multicast or broadcast messages allow addressing a number of building technology devices at the same time, there are typically no acknowledgement messages sent back to the sender from the devices addressed by the broadcast or multicast message to avoid congestion in the network. Hence, the sender has no way of determining whether or not the addressed devices received the sent broadcast or multicast message.